1. Field of the Invention
The present invention relates to a method of charging coke ovens with coal and a coal-charging machine to carry out the same. The invention is applicable in the coking-by-product industry.
Most advantageously this invention can be used for smokeless charging of horizontal coke ovens.
2. Description of the Prior Art
The method for charging coke ovens which is most extensively used at present consists in alternately charging coal to the coke ovens in a predetermined sequence through the charging holes in the oven roof (Nepomniastchiy I.L., Koksovye mashiny, ih konstrukzyi i raschet, Moskva, Metallurgizdat, pp. 135-137).
The number of charging holes in each coke oven, depends on the size thereof and the characteristics of the coal charged, and may be three or four or, more rarely, more than four. Several dozen coke ovens are installed side-by-side and parallel with each other to form a coke-oven battery. Coal from a coal bin generally positioned between two coke-oven batteries is discharged into the hoppers of a coal-charging machine which brings the coal charge to the coke ovens. The coal-charging machine travels on rails laid on the top of the coke ovens along the coke-oven battery. The number of hoppers on the coal-charging machine generally corresponds to the number of charging holes in the coking chamber, the hoppers being arranged on the coal-charging machine in one row parallel to the coking chamber axis (or perpendicular to the longitudinal axis of the coke-oven battery). Normally, one coking chamber is charged at one loading of the coal charging machine.
Discharging the coal from the hoppers of a coal-charging machine to the coking chamber, i.e. charging the coking chamber is one of the most important and elaborate operations. Since the walls of a coking chamber in which the coal charge is placed are at a temperature higher than 1000.degree. C. the coal charge, as a result of the decomposition of the coal begins to intensely evolve a considerable amount of gases. These gases carry along into the atmosphere, or gas collectors a great deal of dust. At the same time in the charging zone there is formed a dangerously explosive gas-and-dust mixture, which may explode or cause the coal charge to ignite.
In order to prevent, or, at least, decrease the amount of the dust discharged into the atmosphere and carried into the gas collectors communicating with the coking chambers through ascension pipes, there have been applied different methods, such as for example, those procedures which avoid the discharge of the coke-oven gas, dust and coal particles into the atmosphere or alternatively discharging the coal charge from the hoppers of a coal-charging machine (cf. U.S. Pat. No. 3,542,650).
Discharging the coal from the coal-charging machine, is normally done as follows: the coal is discharged first from one of the extreme hoppers, then from the other (i.e. opposite) outer hopper, and finally from the middle one. (In case the latter has three hoppers). In the case of four, five or more hoppers the discharging succession is the same, discharging coal from the next hopper being started after the previous one has been completely emptied. Pouring from the hopper into the coking chamber, the coal piles up therein forming a cone-shaped pile with an angle of rest, the crest of the pile facing the centre of the charging hole. As a result, within the coaking chamber there remain unfilled zones wherein partially settle coal dust, and wherethrough to the ascension pipes are passed the gases evolving from the coal during the charging, thereby precluding the formation of explosive mixture of dust and gas in the charging zone.
The coal in the coking chamber is then levelled by means of a leveling bar mounted on the pusher ram and being introduced into the coking chamber through a port provided in the door located on the coke pusher side of the coking chamber. The opposite side of the coking chamber is called a coke discharge side.
To prevent the gases containing coal dust from passing into the collection mains the latter are cut off from the coking chamber by means of valves mounted in the ascension pipes, and the said gas is discharged into the atmosphere through outlets provided in the ascension pipes by opening the covers shutting these outlets. Thus, the gases evolving from the coal being charged are discharged through the ascension pipes into the atmosphere, which, however does not exclude the danger of ignition or explosion of the said gases immediately above the ascension pipes when they are discharged into the atmosphere.
The danger of gas explosion or ignition can be reduced by speeding up the gas discharging which is achieved by ejecting steam or water in the direction of the gas discharge (A. B. Hadjioglo et al. Bezdymnaya zagruzka koksovyh pechei. Moskva, "Metallurgiya," 1978, pp. 47-48). However, this method remedies the problem only partially.
To improve the explosion safety of the charging operation effected in the above sequence, the gases evolving from the coal charge during the charging thereof are passed to a gas-purifying apparatus (cf. Patent of Japan No. II, 987/67).
The disadvantage of this method lies in that the gas flow crosses the flow of coal being charged. In addition, a considerable amount of coal particles are entrained by the gases being withdrawn and is burned therewith. This not only causes a loss of the coal charge but also increases operating load of the burning chamber, and causes the latter to be clogged with ash and slag without remedying the problem of eliminating the danger of explosion.
It is known that attempts have been made to decrease explosion hazard by changing coke ovens through pipes with the aid of a carrier such as steam, inert gases, etc. (cf. U.S. Pat. Nos. 3,047,473; 3,432,398; 3,374,151, and French Pat. No. 2,084,051).
In practice, however, the coal to be charged through pipes must be preliminary dried, in which case the dried coal becomes liable to start burning and explode. Therefore, this method does not yield desirable results.
Furthermore, together with the coal charge a large amount of the carrier gas is blown into the coking chamber. The carrier gas is at a lower temperature than the temperature within the coking chamber. The large amount of cold gases not only causes the coke oven to be prematurely rendered inoperative because of sharp temperature changes, but greatly increases the amount of gases and dust to be withdrawn from the coking chamber. In addition, the apparatus for carrying out this method features a rather complex construction.
There is also known a method of charging coke ovens with coal (U.S. Pat. No. 4,071,414), which comprises pouring coal through the extreme charging holes of the coking chambers and simultaneously withdrawing the gases evolving from the coal being charged, holding the coal charge over a time period sufficient for a coal-charging machine to deliver a next batch of coal to the next coking chamber to be charged which is to be completely charged through its middle charging holes while simultaneously withdrawing the gases evolving from the coal being charged, completely charging the coking chamber simultaneously with the charging of the next successive coking chamber through the extreme charging holes thereof. The gases evolving from the coal charge during the charging thereof are withdrawn through ascension pipes disposed on the both sides of each coking chamber, i.e. the coke pusher side and the coke discharge side. The direction of the gas flow in the coking chamber is periodically changed: when the coal is poured from the extreme hopper located on the coke pusher side of the coke oven battery, the gases are withdrawn through the ascension pipe located on the coke discharge side, and on the contrary, when the coal is discharged from the extreme hopper located on the coke discharge side the gases are removed through the ascension pipes on the coke pusher side of the coke oven battery.
The above method of charging coke ovens, in comparison with the aforementioned ones, somewhat reduces the probability of formation of the dangerously explosive mixtures of gas and dust within the charging zone due to a reduced amount of dust entrained by the gas being withdrawn. In addition, the above process of two-step (charging and then completely charging) charging coke ovens in comparison with the conventional ones takes less time, which results in a smaller amount of gases being evolved and, hence, a smaller amount of coal particles and dust are entrained thereby and discharged into the atmosphere. With two coking chambers charged simultaneously, the flow of the gas and the coal charge is distributed so that the rate of formation of the coal dust at the moment of the coal being discharged from the hoppers is reduced. Furthermore, during the holding period taking place between the two successive charging operations the coal charge in the coking chamber becomes more compacted, which in turn improves the efficiency of the charging process.
The above-mentioned Patent also discloses a coal-charging machine comprising hoppers disposed on a frame mounted on carriages: the extreme end hoppers for charging one coking chamber through the extreme end charging holes thereof and the middle hoppers for completely charging through the central charging holes the other coking chamber already partially charged through its extreme charging holes. The hoppers have in their upper part a feed means wherethrough the coal is passed from the coal bin into them, and in their lower part discharge means wherethrough the coal is passed from them into the coaking chambers. The gases evolved from the coal charge during the charging thereof are withdrawn through the ascension pipes located both on the coke pusher side and the coke discharge side of the coking chamber. The centres of the discharging holes of the extreme end hoppers are displaced relative the centres of the discharging holes of the middle hoppers for a value equal to the distance between the longitudinal axis of the coking chamber being charged and of the coking chamber being completely charged. This permits the charging cycle to be reduced at the expense of simultaneously carrying out said operations without additional maneuvering the coal charging machine relative to the coking chambers being charged. In addition, as have been already mentioned, the amount of gases discharged into the atmosphere is also reduced since with the two-step charging method the coking chamber is cut off from the gas collection system and communicates with the atmosphere for a shorter period of time. Therefore, the amount of air which gets inside the coking chamber during the charging thereof and which forms together with the coke gas an explosion mixture is also reduced.
However, the discharge of gases through ascension pipes which communicate with the atmosphere does not exclude the possibility of ingress of the air into the coking chamber and hence the formation of the dangerously explosive gas and coal dust mixture within the coal charging zone. Furthermore, at some coking-by-product plants the content of nitrogen oxides in the gases being withdrawn exceeds allowable ones, which limits the application of the coke-oven gas. For instance, using coke-oven gases with a high content of nitrogen oxides in the production of nitrogen fertilizer may be a cause of explosion.